This invention relates broadly to a method of and apparatus for changing magnetic forces. More particularly, it relates to method and apparatus wherein the magnetic forces generated by and between a pair of magnetic assemblies spaced apart along a given path are changed.
Apparatus employing interacting magnetic fields for generating motive forces are well known. One rather conventional kind includes a bobbin about which is wound one or more field coils. Mounted within the bobbin is an armature which may be comprised of a core formed from a piece of soft iron, as shown in U.S. Pat. No. 3,728,654; or a plurality of permanent magnets, as shown in U.S. Pat. Nos. 3,022,400, 3,202,886 and 3,495,147; or a combination of a core and a permanent magnet. Application of current in one direction to the field coil generates a magnetic field which interacts with the armature to drive the latter in one direction. Reverse application of the current causes the armature to be driven in an opposite direction.
Another kind is disclosed in applicant's commonly-assigned U.S. Pat. No. 4,265,530. In this patent, shutter blades are driven by a motor having an armature including a pair of spaced apart permanent magnets having common poles facing each other which create a magnetic field that intersects a field coil. Energization of the field coil results in movement of the armature.
Still another known actuator includes a pair of spaced apart permanent magnets having poles facing each other by a predetermined distance. A core piece is movable between the poles in response to field coils either diminishing or increasing the field strengths of the facing poles.